JP4204557B2 - Image forming apparatus and image forming method - Google Patents

Description

2. Description of the Related Art When driving at night with an automobile, the reach of the low beam is limited, so that the driver's view is reduced. In recent years, the introduction of new gas discharge headlamps with more powerful light emission has improved the illumination of the roadway over conventional headlights. However, the field of view is also limited by such new headlights, and therefore attempts have been made to use night night vision systems in automobiles to improve visibility.

  Night night vision systems can be divided into passive night night vision systems and active night night vision systems. A passive night vision system consists of a thermal imaging camera. A drawback of passive night vision cameras is that some thermal imaging cameras have difficulty in forming realistic images. In contrast, an active night night vision system consists of an illumination unit that emits infrared radiation (eg, a halogen light with a filter) and one or more infrared cameras. The lighting unit illuminates the front area of the vehicle in the high beam area, the camera records the reflected infrared high beam and reproduces this image on a monitor or head-up display. Here, headlights for visible low and high beams are used to emit infrared light. Increasingly, however, in the automotive industry, infrared-emitting halogen headlights are replaced by infrared-free xenon headlights. This requires a radiation source that emits additional infrared radiation. As an additional infrared radiation source, for example, an infrared radiation laser is used.

  German patent DE 4243200 C2 describes a friendly-enemy-identification device for military agricultural vehicles. A thermal imaging camera with a CO2 laser is coupled to visualize hidden signs for ally-enemy-identification. The observer sends out individual light pulses and the infrared camera receives the reflected signal synchronously. The disadvantage of this device is that the thermal imaging camera does not actually provide a faithful image. No suggestions are given in DE 4243200 C2 regarding an apparatus and a method for forming realistic images that are suitable for use in automobiles.

Advantages of the Invention An image forming apparatus and method in an automobile described below in the form of forming an image for each image row in synchronization with pulsed illumination around the automobile by at least one infrared camera is as follows. Has advantages. In other words, it is an advantage that an image that is high in image quality and faithful to reality can be formed regardless of whether the visibility situation and / or the weather is good or bad. This image forming apparatus and method particularly advantageously contributes to reducing the number of accidents during poor visibility conditions (especially at night) due to the high quality of the formed images. Really faithful images with high image quality are formed by the following even when the visibility and / or weather conditions are bad. That is, it is formed by the fact that the illumination of the image detection area by the radiation source emitting at least in the near-infrared spectrum area is not significantly disturbed by rain or snow.

Advantageously, the lifetime of at least one radiation source emitting in at least the near-infrared spectral region is increased by pulsed light radiation. At the time of pulse driving, when the output is the same, the heat load of the radiation source is smaller than that during continuous operation. This directly extends the life. The longer life of the radiation source, and thus the longer exchange interval, advantageously reduces the operating costs in the case of motor vehicles.

  At the same time, the pulse driving of the at least one infrared radiation source allows a much higher radiation intensity in the light pulse if the radiation intensity of the radiation source is on average the same. Here, the radiation intensity is determined as an output per solid angle. Therefore, the irradiance of the irradiated area, ie the output per area, is increased during the light pulse compared to continuous non-pulsed light emission. Particularly advantageously, this intensively illuminates the image detection area of at least one infrared camera.

  Particularly advantageously, the at least one infrared CMOS camera forms at least one image around the car. Unlike other types of cameras, CMOS cameras have reduced blooming effects. Here, blooming means that the formed image is clouded (Ueberstrahlung) due to dazzling by a strong light source.

  Particularly advantageously, the image detection area of the at least one infrared camera can be illuminated in a pulsed manner by means of at least one infrared emitting laser and / or at least one infrared emitting laser diode. For example, laser diodes allow the generation of short light pulses with a short response characteristic under simultaneous high radiation intensity during the light pulse duration. Further, the infrared radiation laser and / or the infrared radiation laser diode has the following advantages. That is, it is an advantage that the laser beam has a narrow spectral bandwidth. It is possible to filter out other spectral regions by means of a corresponding band filter in front of at least one infrared camera. For example, in the case of an oncoming vehicle traveling with a low beam at night, this makes it possible to filter out such visible light that becomes an obstacle to image formation. By using at least one infrared emitting laser and / or at least one infrared emitting laser diode, an image with high image quality is formed. In addition, infrared emitting lasers and / or infrared emitting laser diodes have the advantage of high efficiency.

A radiation source emitting at least in the near infrared spectral region forms a light pulse. Advantageously, the pulse duration of the light pulse is shorter than 100 ns, in particular between 10 and 80 ns. Such a short pulse duration enhances the quality of the formed image. As an alternative or additionally, light pulses with a duty factor of preferably less than 0.1% are formed. With such a technique, high irradiance is generated during the light pulse, which results in good image quality.

In the case of synchronization for each image row, the detection of the image row of at least one infrared camera is synchronized in time with the pulsed illumination. Here, temporal synchronization is performed for each image row or a sequence of at least two image rows. Such a temporal synchronization for each image row of the image row detection with the pulsed illumination advantageously provides a reliable and time-stable synchronization. On the other hand, temporal synchronization for each image or each image sequence (bildfolgenweise) has the following advantages. That is, there is an advantage that the technical cost for synchronization is reduced. Temporal synchronization is performed on at least one image under temporal synchronization for each image or image sequence. Such synchronization per image row or per image or per image sequence is on at least one synchronization line between at least one infrared camera and at least one radiation source emitting in at least the near infrared spectral region. Obtained by a one-way or two-way synchronization signal. The temporal synchronization is particularly preferably performed via at least one communication data bus in the vehicle, for example a CAN bus. This advantageously eliminates additional synchronization lines and uses the existing infrastructure in the vehicle for data exchange.

The autonomous temporal synchronization of at least one infrared camera with pulsed illumination is particularly advantageous. This is because there is no need for a separate synchronization line between at least one infrared camera and at least one radiation source emitting in at least the near infrared spectral region . This has the following advantages. That is, the apparatus and method described below have the advantage of being resistant to noise. This is because the individual components operate independently of each other.

  The variants of the apparatus and method described below have the particular advantage that the detection of the image rows can be shifted in time with respect to the pulsed illumination. This compensates, for example, the propagation time effect of the beam from light pulse emission to detection by the camera. As a result, an image having high image quality is obtained.

  Another variant of the apparatus and method described below is advantageous in that the temporal synchronization is performed in dependence on at least one image quality level (Bildqualitaets masses). By calculating at least one image quality level, on the one hand, the time lag between image row detection and pulsed illumination is automatically adjusted. Similarly, this creates an image with high image quality. This is because image exposure in the entire image area and image sequence is constant. In addition, by ascertaining at least one image quality level, autonomous temporal synchronization of at least one infrared camera and pulsed illumination is possible. This is done by shifting the detection of the image row relative to the pulsed illumination when the image quality level deteriorates to obtain a high image quality.

  Further advantages are described in the following description of embodiments and the dependent claims with reference to the drawings.

The invention will be described in more detail on the basis of the embodiments illustrated below.

FIG. 1 is an overview of the first embodiment.
FIG. 2 is a block diagram of the first embodiment.
FIG. 3 is a time diagram of the first embodiment.
FIG. 4 is an overview of the second embodiment.

Description of Examples Hereinafter, an image forming apparatus and an image forming method in an automobile will be described. The infrared camera forms an image of the periphery of the car in an image row for each row. The image detection area of the infrared camera is illuminated in pulses by a radiation source that emits in at least one near infrared spectral region . Image row detection is performed in time synchronization with pulsed illumination. In the first embodiment, the detection of the image row of the infrared CMOS camera is synchronized in time with the laser diode radiating in the near-infrared spectral region via the synchronization line. In the second embodiment, the detection of the image row of the infrared CMOS camera and the temporal synchronization with the pulsed illumination are performed autonomously by evaluating at least one detected image row with the CMOS camera. .

FIG. 1 shows an overview of the image forming apparatus in the automobile of the first embodiment. This consists of an infrared camera 10 having a control unit / processing unit 16 and a radiation source 12 emitting in the near infrared spectral region having a control unit 14. The control unit / processing unit 16 of the infrared camera 10 and the control unit 14 of the radiation source 12 are connected to each other via a signal line 18. The radiation source 12 generates infrared light 20 in the near infrared spectral region , which illuminates the periphery 24 of the vehicle in pulses. Here, the radiation source 12 is integrated in the front area of the vehicle between the low beam / high beam headlights. In the first embodiment, a laser diode that emits light in the near infrared spectral region is used as the radiation source 12 that emits light in the near infrared spectral region . The radiation source 12 is controlled and monitored by a control unit 14. From the infrared rays 22 that are scattered back, the infrared camera 10 forms an image of the periphery 24 of the automobile. The infrared camera 10 is attached to the area of the indoor rearview mirror behind the windshield of the automobile. In the first embodiment, the infrared camera 10 is an infrared CMOS camera 10. The CMOS camera 10 is driven and controlled via a control unit / processing unit 16. At the same time, the CMOS camera 10 transmits the formed image of the car periphery 24 to the control unit / processing unit 16 for further processing.

FIG. 2 shows a block diagram of the image forming apparatus in the automobile of the first embodiment. In the following, the operation of additional components and devices with respect to FIG. 1 will be described. The radiation source 12 radiating in the near infrared spectral region has a laser diode 28, a photodetector 30, and a temperature independent resistor 32 radiating in the near infrared spectral region . The laser diode 28 is driven and controlled depending on the measurement value obtained by the photodetector 30 and the temperature-independent resistor 32 via a signal line 38 for laser diode drive control. The photodetector 30 and the temperature independent resistor 32 are used in the feedback coupling branch as measurement means. This adjusts the radiation intensity and / or temporal characteristics of the light pulse output by the laser diode 28 with closed loop control. The radiation source 12 generates infrared radiation at least in the near infrared spectral region , preferably in the wavelength region between 850 nm and 900 nm. Subsequently, the generated infrared rays are used to illuminate the image detection area of the CMOS camera 10 in a pulsed manner via the lens 26. The lens 26 is used to expand the generated infrared rays in the vertical and horizontal directions, and the image detection area of the CMOS camera 10 is illuminated as completely as possible. The infrared rays reflected and returned are detected by the infrared CMOS camera 10 after filtering by the filter 27. The filter 27 is a band filter that transmits transmitted infrared wavelengths and attenuates wavelengths outside the passband. The infrared CMOS camera 10 forms an image of the periphery of the automobile from the infrared rays reflected and returned, and transmits the formed image to the control unit / processing unit 16 via the signal line 36. The infrared CMOS camera 10 consists of individual pixels. The pixels are arranged in a matrix including 640 × 480 pixels in the first embodiment. An image row is detected for each row to form an image. Here, the CMOS camera 10 buffers and stores the image signal for each row. As a result, the flash emitted from the radiation source 12 gradually irradiates the entire image for each row. Moreover, no laser energy is emitted in a phase that does not respond to exposure. The photosensitivity for each row of the CMOS camera 10 is also referred to as “row shutter”. Via the signal line 18 and the signal line 34, the control unit / processing unit 16 controls the temporal synchronization between the detection of each image row and the pulsed illumination of the image detection area of the CMOS camera 10. In the first embodiment, unidirectional temporal synchronization is performed. The control unit / processing unit 16 outputs a row signal to the CMOS camera via the signal line 34. In synchronization with this, a laser control signal is transmitted from the control unit / processing unit 16 to the control unit 14 of the radiation source 12 via the signal line 18. When each row signal reaches the CMOS camera via the signal 34, the image row is driven and controlled as follows. That is, drive control is performed so that an image row reacts to optical information. The optical information is converted into an image signal through a sample and hold circuit. After the sampling process is completed, the connection is automatically switched to the next image row, or to the first image row of the matrix when the last image row is reached. When this is followed by a row signal, the above process is repeated and the sampling process for this image row is performed accordingly. The image is finally composed of image signals for each pixel in the entire image row. The control unit 14 generates a laser control current from a laser control signal transmitted via the signal line 18. This is used for direct drive control of the laser diode 28 via the signal line 38 for laser diode drive control. In some cases, the phase shift between the pulsed illumination of the image detection area of the CMOS camera 10 and the detection of each row of the image row to be synchronized in time is a pulse to the CMOS camera 10 and the control unit 14, i.e. Compensated by shifting the row signal and laser control signal in time. The cause of the phase shift includes a time delay in optical pulse generation and a propagation time delay of the optical pulse. Such deviations are typically fixedly adjusted depending on the individual components being used. Alternatively, this deviation is obtained via the image quality level. The image quality level is determined via image evaluation in the control unit / processing unit 16 with respect to the luminance of the image and / or the luminance gradient at the image edge, ie the luminance gradient in the direction from the first image row to the last image row. Desired. The time offset is set optimally depending on the image quality level determined in the control unit / processing unit 16 via a corresponding closed-loop control.

  3 shows a time diagram for the first embodiment of the signals 40, 42, 44 on the signal lines 34, 18, 38 shown in FIG. 2, respectively, and the laser pulse 46 of the infrared 20 shown in FIG. The time course characteristics of are shown. FIG. 3 shows the basic characteristics of the signals 40, 42, 44 and the laser pulse 46. On the abscissa of FIGS. 3a, 3b, 3c and 3d, time t is shown respectively. FIG. 3a shows the voltage U of the row signal 40 on the signal line 34 shown in FIG. A pulse having a period of 100 μs and lasting about 120 ns is generated as the row signal 40. Row signal 40 is used in a CMOS camera to perform the sampling process and simultaneously select the next image row. FIG. 3b shows the voltage U of the laser control signal 42 on the signal line 18 shown in FIG. A pulse lasting about 80 ns with a period of 100 μs is generated as the laser control signal 42. The laser control signal 42 is used as a signal for the control unit 14 shown in FIG. This produces a laser control current 44 depending on this laser control signal 42. This is then converted into a laser pulse 46 by the radiation source 12 emitting infrared radiation as shown in FIG. FIG. 3c shows a time course characteristic of the current I of the laser control current 44 on the signal line 38 shown in FIG. Finally, FIG. 3 d shows the time course characteristic of the radiant flux Φ of the laser pulse 46. 3a and 3b show the time lag Δt between the start of the pulse of the row signal 40 and the start of the pulse of the laser control signal 42. FIG. In the first embodiment, this time shift Δt is adjusted as follows. That is, the pulse of the laser control signal 42 is adjusted symmetrically so as to be positioned at the center of the pulse of the row signal 40. Correspondingly, the time shift Δt is about 20 ns in the first embodiment.

  In the modification of the first embodiment described above, an image synchronization pulse is output from the control unit / processing unit 16 shown in FIG. The image synchronization pulse defines the start of image detection for each row in the first image row. The infrared CMOS camera 10 generates a row signal 40 triggered by an image synchronization pulse by its own clock generator itself. In analogy to this, the control unit 14 is triggered by an image synchronization pulse by its own clock generator itself to generate the laser control signal 42 in the same way. In this variant, quartz is used as the clock generator. In another variant, temporal synchronization is performed for each image sequence. That is, an image sequence synchronization pulse is formed after, for example, 10 images, and the CMOS camera 10 and the control unit 40 generate the row signal 40 and the laser control signal 42 in the meantime by a unique clock generator. In another variant of the embodiment described above, temporal synchronization is performed in both directions.

FIG. 4 shows an overview of the image forming apparatus in the automobile of the second embodiment. It consists of an infrared camera 10 having a control unit / processing unit 16 and a radiation source 12 emitting in the near infrared spectral region having a control unit 14. In the following, only the difference in configuration and function of FIG. 4 from FIG. 1 will be described. Unlike the first embodiment shown in FIG. 1, there is no synchronization line. The temporal synchronization between the detection of each image row and the pulsed illumination is performed by determining the above-mentioned image quality level by the control unit / processing unit 16. Depending on the image quality level determined, the control unit / processing unit 16 causes the start of the row signal in order to obtain a high image quality level. Here, the pulse pattern of the radiation source 12 supports the search for the start of the row signal according to the image quality level. Here, the pulse pattern is a frequency change in which the laser pulse fluctuates. Alternatively or additionally, this search is supported by a systematic frequency shift of the row signals and / or image sync pulses and / or image sequence sync pulses.

In the above-described embodiments and modifications, the infrared camera and the camera control unit / processing unit constitute one unit. As an alternative or in addition, the radiation source emitting at least in the near-infrared spectral region and the control unit of the radiation source constitute one unit.

  Variations on the devices and methods described above typically use at least one infrared camera. This has means for detecting an image row for each row. In addition to the infrared camera, in one variant, at least one other infrared camera, in particular at least one infrared CMOS camera, is used. In addition to the 640 × 480 pixel camera matrix size (VGA format) used in the above-described embodiments, in another variation, for example, 352 × 288 pixels (CIE format) and / or 1024 × 768 pixels and / or An infrared camera having a matrix size of 1280 × 1024 pixels is used. In another variation of the apparatus and method described above, image sequences are detected instead of image rows. At least one infrared camera used in the above-described embodiments has a linear exposure characteristic curve and / or a logarithmic exposure characteristic curve.

The pulse duration and / or period of the light pulse is generally adapted to the timing of at least one camera and / or the time characteristics of at least one pixel of at least one camera, according to an embodiment. The camera timing is determined by the image repetition frequency (frame rate) and / or the row synchronization signal and / or the pixel clock. For example, in the case of an image repetition frequency of at least 25 images per second, a pixel clock of 4 MHz to 20 MHz is set according to the matrix size of the infrared camera. The period of the light pulse is between 50 μs and 100 μs, corresponding to the row synchronization signal, depending on the matrix size of the infrared camera. The temporal characteristic of a pixel is the output signal of the pixel on a short, rectangular light pulse. In order to drive a radiation emitting in the near infrared spectral region in a pulsed manner with the highest possible peak radiation output, the duty factor (duty cycle) is chosen as small as possible, preferably less than 0.1%. Limited by the rising characteristics of the pixel, the pulse duration of the light pulse is selected as follows. That is, the pulse duration is selected to be at least 1 pixel-clock. Depending on the matrix size of the infrared camera, the pulse duration of the light pulses is preferably selected between 50 ns and 200 ns.

In addition to the radiation source emitting in the near infrared spectral region in a variant of the apparatus and method described above, at least one other radiation source emitting in the near infrared spectral region is used. Alternatively or additionally, a laser emitting in at least one near infrared spectral region is used. Generally, suitable for outputting infrared radiation at least the near infrared region to the pulsed radiation source is used which emits at least one near-infrared spectral region.

1 is an overview diagram of a first embodiment. The block diagram of a 1st Example. The time diagram of a 1st Example. FIG. 3 is an overview diagram of a second embodiment.

Claims (10)

An image forming apparatus in an automobile,
At least one infrared camera for forming at least one image around the automobile;
In the form of having at least one radiation source emitting in the near infrared spectrum region, illuminating the image detection region of the at least one infrared reaction camera in a pulsed manner,
The infrared reaction camera has a row shutter, the camera reacts to light for each row,
Means are provided for detecting at least one image for each row in the image row and performing temporal synchronization of the pulsed illumination and image row detection.
An image forming apparatus in an automobile.   The apparatus of claim 1, wherein the at least one infrared camera is at least one infrared CMOS camera. The apparatus according to claim 1, wherein the at least one radiation source emitting in the at least near infrared spectral region is at least one infrared emitting laser and / or at least one infrared emitting laser diode. Said at least one radiation source emitting in at least the near-infrared spectral region outputs a light pulse having a pulse duration adapted to the time characteristics of at least one pixel of the camera, in particular between 50 ns and 200 ns. 4. A device according to claim 1, comprising means for outputting a light pulse having a pulse duration.   Device according to any one of claims 1 to 4, wherein means are provided for performing the temporal synchronization for each image row and / or for each image and / or for each image sequence.   The apparatus according to any one of claims 1 to 5, wherein the at least one infrared camera has means for autonomously performing temporal synchronization with the pulsed illumination. An image forming method in an automobile,
At least one infrared camera, in particular at least one infrared CMOS camera, forms at least one image of the periphery of the vehicle;
At least one radiation source emitting in the at least near-infrared spectral region , in particular at least one infrared emitting laser and / or at least one infrared emitting laser diode, pulses the image detection region of the at least one infrared camera. In the form of a method of illuminating
Detecting the at least one image in an image row for each row;
Synchronizing the detection of the image row in time with the pulsed illumination,
An image forming method in an automobile. At least one radiation source emitting in at least the near infrared spectral region outputs a light pulse having a pulse duration tailored to the temporal characteristics of at least one pixel of the camera;
8. The method as claimed in claim 7, wherein in particular at least one radiation source emitting in at least the near infrared spectral region outputs a light pulse having a pulse duration of between 50 ns and 200 ns.   The method according to claim 7 or 8, wherein the temporal synchronization is performed for each image row and / or for each image and / or for each image sequence.   10. A method according to any one of claims 7 to 9, wherein the at least one infrared camera is autonomously synchronized in time with the pulsed illumination.

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